1. Field of the Invention
The present invention relates generally to liposomes, and more particularly to liposomes which encapsulate fluid materials, such as drugs, nucleic acids, proteins and the like, and which selectively release the fluid contents thereof in response to irradiation with light.
2. Prior Art
Liposomes are unilamellar or multilamellar lipid vesicles which enclose a 3-dimensional space. They are well recognized as useful for encapsulating therapeutic agents, such as cytotoxic drugs or other macromolecules capable of modifying cell behaviour, and carrying these agents to in vivo sites. For example, U.S. Pat. No. 3,993,754, inventors Rahman et al, issued Nov. 23, 1976, discloses an improved method for chemotherapy of malignant tumors in which an antitumor drug is encapsulated within liposomes and the liposomes are injected into an animal or man. Drug administration via liposomes can have reduced toxicity, altered tissue distribution, increased drug effectiveness, and an improved therapeutic index.
Liposomes have also been used in vitro as valuable tools to introduce various chemicals, biochemicals, genetic material and the like into viable cells. However, a serious deficiency of liposomal drug delivery has been the inability to quantitatively or selectively direct the liposomes' contents to specific sites of action over a therapeutically meaningful time frame. Use of temperature sensitive liposomes has been proposed as a possible solution to the problem. For example, temperature sensitive liposomes have been suggested for in vivo use to release methotrexate to particular sites in mice by heating the area where drug delivery was desired.
The present invention is directed to overcoming one or more of these problems.